This story is a sequel to my HP/SG-1 crossover Harry Potter and the Chappa'ai. Following the defeat of Anubis SG-1 and their wizading friends are called to assist Atlantis to fight off a Wraith attack.

It was late in September and it had been three months since Gawain had been lost in the Pegasus galaxy. Based on the reports posted after the mission and the hearing at the Ministry Kingsley had concluded that Gawain's actions could be considered somewhat reckless, but given the situation no one had opted for a reprimand and no one blamed the other team members. Harry, Ron and Hermione still felt there should've been something more they could've done to save Gawain. Now it was September and there'd been no news from Atlantis. Harry had spent most of the summer at the Burrow with Ginny, and with Ron and Hermione of course. The summer months had done miracles for their relationships and coming to terms with their war experiences. All four had received a Hogwarts letter inviting them to the seventh year. Ginny and Hermione had also received the Quidditch captain's badge and Head Girl badge respectively. Headmistress Minerva McGonagall had added a personal letter to Harry and Ron. She explained that she considered them both for Head Boy, but unlike Hermione she felt less certain if either of them would return for their NEWT year. In the end Ron had decided to join George rebuilding Weasleys' Wizarding Wheezes apart from his work for the Ministry. Harry had been convinced by Kingsley to work for the Ministry. Officially he held a position as a junior employee at the Department of Magical Law Enforcement. In reality he was leading the cooperation with the Muggle Americans and SG-M. With Hermione and Ginny at Hogwarts Harry and Ron slowly found a routine. They both lived at the Burrow and worked in London. Every weekend they met with their girlfriends in Hogsmeade. Hermione had an agreement with professor McGonagall that she would join Harry and Ron if SG-M was called into action. They hadn't given up on Gawain.

This particular day Harry was called to SGC and it was some time after lunch he was transported to Cheyenne Mountain.

"Good morning Harry." Jack greeted him with a yawn, holding a cup of coffee.

"You're asking me that?" Jack asked "All I know is that Doc Frasier got a delivery last evening from Pegasus and has been here all night, asked me to get you here and call to a meeting. We're going to the infirmary where SG-1 and Hammond are waiting."

Jack and Harry entered the infirmary where Dr Frasier stood next to a dead Wraith.

"Welcome Harry." general Hammond said and turned to Dr Frasier "Doctor, if you please. Why are we here?"

"I got this dead Wraith from Atlantis, because Dr Beckett wanted someone with more experience of researching magic to take a look." Dr Frasier began "And I'm fairly certain this Wraith was killed by magic."

"Gawain?" Harry asked with a renewed hope that they'd bring him back.

"There's a total lack of injury, no poison, pathogens or anything else that explains why he's dead." Dr Frasier continued.

Harry nodded, recognising the description.

"The Killing curse then." he concluded.

Dr Frasier agreed.

"That's my conclusion, since that's the only thing we know of that kills without leaving any clue. I still don't fully understand the Killing curse, but somehow negative emotions like hate or anger along with the incantation and wand movement produces a burst of anti-life, lacking a better word." Dr Frasier said "Any contact with a living organism causes the anti-life and life to erase each other without and trace of either left. But we also know that an unconditional love, such as Harry's mother displayed by sacrificing her life protected Harry. I have no idea how this protection works, or if it's possible to develop into a defence, that won't require the sacrifice of one life to save another."

"Shepperd's team came across a hive, dead in space, and it wasn't the one that attacked Atlantis. This fellow comes from that hive."

"So Gawain escaped and is still out there somewhere?" Harry asked.

"The thing is that our Wraith here wasn't the only one. In fact every Wraith on the hive was dead. What's more, the organic-based systems on the hive were also, lacking a better word, dead." general Hammond explained.

Harry gasped.

"Are you saying an entire hive was AKd?" he asked.

"That's what we think." Dr Frasier said.

"But it's not possible." Harry said "Not even a Dark Wizard as powerful as Voldemort would be able to cast thousands of Killing curses in such a short time."

"Why is that?" Dr Frasier asked.

"Casting spells is exhausting. Just like physical activity strains the body, magic strains our core. Too much and too powerful magic in a short time will exhaust us." Harry explained "We can do normal magic all day, but extremely powerful spells like the Killing curse would exhaust any wizard."

"Nevertheless we have a hive with crew that seems to have been collectively AKd." general Hammond concluded "I'd like SG-M and SG-1 working with Shepperds team in order to find out what happened, and if possible rescue Gawain."

"Should I ask for a replacement for Gawain, or will it be me, Ron and Hermione?" Harry asked.

"One more question general." Harry said "Have the Unspeakables made any progress on the magic imbued in Atlantis?"

General Hammond nodded.

"They have uncovered several city wide charms. In fact I'd like to send a request with you to Kingsley, asking for an Unspeakable permanently assigned to Atlantis. The magic will greatly strengthen the defensive capability of the city." he said "Anything else?"

They all shook their heads.

"Dismissed." general Hammond said and approached Harry "If you'll come to my office before you leave I'll give you the request to Kingsley."

Harry and general Hammond left together.

"This is the first sign of anything magically related, suggesting Gawain is still alive, but I'm still not entirely happy about the news." Harry said.

"I know." general Hammond agreed "And since you say that one wizard couldn't have caused this it must be investigated. The Killing curse is one of the worst weapons I've ever heard of, and we are defenceless against it. Evidently the Wraith hive was defenceless too. The only good piece of news is that you're living proof of the fact that it is possible to be hit and survive."

Harry nodded in agreement.

"And the bad news is that we have absolutely no idea how we develop a defence." Harry added.

General Hammond only sighed, as he opened his door. After accepting an envelope Harry returned to the transportation site, to deliver it before he headed to Diagon Alley where Ron should be.

It was late in the afternoon and the shops in Diagon Alley prepared to close for the day when Harry entered Weaselys' Wizarding Wheezes. Ron, George and Verity were there tending to the last customers of the day.

"Harry my friend. How's the Ministry today?" Ron asked.

"Harassed by memos as usual, and that syrupy bint in the lift is as polite as ever." Harry grinned.

Ron shook his head.

"Honestly Harry, you should've accepted only part time in that place like me. I actually have fun working here, which makes the Ministry bearable."

"Yes, really Harry. If you'd work in the Hogsmeade shop you'd be closer to Ginny, and everyone would go there to buy Harry Potter's favourite pranks." George added.

Harry really disliked the hero status he'd been given after defeating Voldemort, which George knew very well.

"Prat." Harry replied.

"And proud." George countered with a grin "Ron, Verity and I can close up for the day. You go with Harry."

"Thanks bro'" Ron said.

The two friends left the shop.

"We need to talk." Harry said "Let's go home."

They turned and Disapparated with a soft pop. Outside the Burrow's wards they Apparated and walked the short distance to the house. They could smell Molly's supper from the garden.

"Hello Mum." Ron greeted "What's for supper?"

"Just a simple pie." Molly said.

"It smells delicious." Harry added.

"It'll be ready when Arthur comes home in about half an hour." Molly told them.

"All right, we'll be upstairs." Harry said and headed up to Ron's room.

Once inside Harry told Ron about the day.

"But after leaving the SGC I got an idea.." Harry said "I think Doc Frasier should examine me and Ginny."

Ron looked dubiously at Harry.

"Why?" he asked.

"Because I gave my life for her when I took the Killing curse Voldemort cast on me."

"And you survived because your mother's protection still was active after Voldemort took your blood."

"That is true, but the fact remains. Ginny is the only one who's been protected against the AK where the one willing to sacrifice his life survived. And that's what we want, a defence not claiming anyone's life."

Ron wasn't keen on the idea to involve his little sister in their work for SGC. She did know they worked with American Muggle military and had met SG-1 when they'd visited the Burrow, but she had no idea about the Stargate.

"And with Voldemort gone that protection is gone." Ron argued.

"True, but let's face the facts Ron. Something out there AKd an entire hive. I know an examination of Ginny and me might not reveal anything, but there is still a chance, and I think we must take it."

Ron nodded reluctantly, since Harry made a good point.

"But she's not going with us to Pegasus." Ron said.

"I don't want to put Ginny in any kind of danger, you know that." Harry said "But she's also of age."

"I'll support the idea to bring her to Doc Frasier." Ron said "Let's clear this with Kingsley first thing tomorrow, before we leave for SGC.

"We'll have time to Floo there and be back in time for supper." Ron decided and hurried downstairs.

Molly was setting the table and looked inquisitively at them when they headed for the fire place.

"We'll be back for supper Mum." Ron promised and tossed Floo Powder into the fire. "Minerva McGonagall's office."

A few moments later the headmistress had cleared them to Floo to her office.

"Good evening Harry and Ron." professor McGonagall greeted them as they stepped out of the Floo.

"Good evening professor." they replied.

"Goodness. It's Minerva. I'm not your professor any longer." she said "What can I do for you?"

"We need to bring Hermione along with us tomorrow, and provided Kingsley approves of it, we need Ginny too."

"Ginny? What for?" professor McGonagall asked.

Harry explained that there was a chance to maybe learn something about the Killing curse and come one step closer to a defence against it.

"Of course she can go, but don't make a habit out of it." the professor said.

Professor McGonagall didn't know exactly what kind of work they did, but Kingsley had explained that it was very important and if they requested her assistance it would be appreciated if she'd be willing to give it. Harry and Ron nodded and left her office to catch Hermione and Ginny in the Great Hall before supper was over. They quickly located the two witches sitting together at the Gryffindor table.

"Ginny" Harry said softly as he approached her.

She turned around with a smile on her lips.

"Harry, what are you doing here?" Ginny asked and gave him a hug and a quick kiss.

Hermione welcomed Ron in a similar way.

"We need you tomorrow 'Mione." Ron said.

Hermione simply nodded. She understood what it was all about and the professors would assist her to catch up with the lessons she missed.

"And we need you too Ginny." Harry added.

"Me?" she asked.

"We can't tell you too much here, but it involves our colleagues." Harry said, which clarified that it had to do with the American Muggles.

"I wish we could stay, but Molly is about to finish supper, so we better get back home." Harry said.

After a few more kisses Harry and Ron left Hogwarts and headed for the Burrow and supper.

Ginny was looking around the corridors of SCG. She had been cleared to participate in the research concerning the Killing curse and would report to the infirmary along with Harry. Researching the Killing curse seemed more important than ever since it seemed an entire hive had fallen victim to it. "Harry, when are you going to tell me exactly what you need my help with." Ginny asked.

Harry smiled.

"First of all, this place needs something pretty around." Harry said.

"Tosspot." Ginny huffed "But thank you."

"All right, really. We're going to the infirmary to see Dr Frasier, who's the equivalent of Madame Pomfrey around here." Harry said "And she's researching the Killing curse, and if there's a way to defend against it."

"And she's a Muggle?" Ginny asked for clarification.

"Ginny, these aren't your average Muggles. So far we've learned a lot from this cooperation, even the Unspeakables are making sense after being here." Hermione said.

Dr Frasier looked at the two of them. It was hard to believe what they'd been though in the Wizarding war, which she had been fully briefed on in order to better understand the circumstances allowing Harry to survive the Killing curse.

"Ginny, Sam and I will examine you and Harry and take every conceivable reading we can think of. If there's anything left of the protection Harry's sacrifice created, despite Voldemort is dead we hope to find it and try to understand what it is." Dr Frasier explained.

Ginny nodded.

An hour later Ginny and Harry had submitted to MRI and CT scanning, blood samples and a whole battery of tests.

"There it is, do you see it Janet?" Sam asked.

"Are you sure it's not a glitch?" Dr Frasier replied.

"I don't think the same glitch would occur in both Harry and Ginny at the same time." Sam reasoned.

The two of them continued to debate something obviously significant, but Harry and Ginny didn't understand a word of it..

"I think we need to gather the team in the briefing room." Sam decided and called general Hammond.

Ten minutes later SG-1, SG-M (along with Ginny) and Dr Frasier where gathered in the briefing room.

"Doctor, if you please." general Hammond said.

Dr Frasier displayed a set of images.

"As you know we have examined both Harry and Ginny, since they both have been protected from the Killing curse through the ancient blood magic that saved Harry's life as a baby. We didn't expect to find anything conclusive this fast but we think we have made an important discovery." Dr Frasier said and turned to Sam.

"If you look at this first image it's a faint pattern we found in the same part of both Harry's and Ginny's brains. We have examined Harry before, but obviously missed it. It's easy to dismiss as a glitch, but not when it shows up in a very precise part of the brain in two different people." Sam explained "Janet's or my brains don't show this pattern. Now look at this pattern."

Sam displayed a second image.

"That's from Telchak's healing device, that I dug up this summer." Daniel said and looked at SG-M "I haven't had time to tell you about that one."

"Exactly" Dr Frasier said "Can you see the similarity between the patterns?"

They all nodded.

"As I said earlier, we think the Killing curse is a burst of anti-life, and if it gets any contact with life both are erased without a trace. We know that it takes strong hatred to cast it, along with the incantation and correct wand movement. We know that an unconditional love and willingness to sacrifice one's own life can protect another person. What we haven't had any clue to is how this all works." Sam lectured.

"But now you have a theory." general Hammond asked.

"Not so much of a theory just yet," Sam continued "Janet, can you explain."

"Telchak's device had the power to animate dead tissue, and with research we could also develop the gun we use to kill the still roaming Kull warriors, without depending on our wizarding friends to AK them."

"The fact that Harry and Ginny show this pattern, although faint, is an indication that it's the kind of energy that protects against the Killing Curse."

"And we hope that Telchak's device might be possible to use to develop a defence against the Killing Curse."

"How?" general Hammond asked.

"We don't really know yet." Sam replied "But maybe we can create some kind of shield, a life force shield if you will. And if a Killing curse hits it kills the life force in the shield instead of the intended target."

"That's bloody brilliant." Ron said.

"I couldn't agree more." Jack said.

"Calm down." Dr Frasier said "This is not even a sound theory yet. We need time to research this, develop a force field with this kind of energy and test it. One thing we haven't a clue about is how the blood relates to this. How did the taking of Harry's blood keep the protection alive? But we'll analyse the blood samples."

Daniel looked at Dr Frasier.

"I don't have an answer, but in many ancient cultures blood is the symbol of life. Maybe there's more truth to that than we think."

Dr Frasier nodded.

"Possibly there's some kind of magical aspect we still have to understand." Hermione added. "In Harry's case the protection lived on through his aunt in the first place and she was nowhere near Godric's Hollow when Harry's mum sacrificed her love."

"As long as there's a chance we can defend ourselves Harry's aunt can be precisely where she likes." Jack meant.

"As long as it's not where we are." Harry added with a huff.

"I want all of you on your way to Atlantis." general Hammond ordered "Where research will continue along with reconnaissance missions to learn more about the dead hive."

Ginny looked at Harry.

"Atlantis?" she asked.

"It's a long story." Harry said.

"I thought we agreed Ginny wasn't going." Ron said.

"You said you didn't want her to." Harry replied "I said she's a witch of age."

Ginny loved that Harry finally had realised she was perfectly capable of making up her own mind, although his wish to keep her safe was rather flattering too.

"While our boyfriends work out their protectiveness of us, I'll tell you all about Atlantis." Hermione said.

A couple of hours later SG-1, SG-M, Ginny and Dr Frasier stepped through the Stargate for Atlantis. On the other side they were welcomed by a couple of familiar faces. Colonel Shepperd, Dr Weir, Teyla, Rodney and a rather big fellow were there to greet them.

"Welcome back to Atlantis" Dr Weir said "And this time we're not under attack."

"If we had time we could give you the grand tour, but we have work to do." John added.

"Dr Frasier, your first mission here, Dr Beckett will be glad to have you here" Dr Weir continued and her eyes fell on Ginny "I'm Dr Elizabeth Weir and I command this expedition."

"Ginny Weasley, Harry's girlfriend and Ron's sister." Ginny said "I was protected from the Killing curse when Harry was hit, so Dr Frasier is trying to figure out how that happened."

"All right, you'll be shown to your quarters first. Then I want the research team set up immediately, and that's Dr Frasier, Dr McKay, Lt Col Carter, Miss Weasley and Mr Potter. Dr Beckett will assist if necessary" she ordered "Reconnaissance team, meaning the rest of you, report to the briefing room. We have some clues to work on."

As they left Jack approached John.

"Who's your new team member?" he asked and nodded to Ronon.

"He's a former runner." John said "I guess it's a kind of Wraith sport. They put a transmitter inside you, giving away your position, then they hunt you. Just for fun."

"Didn't their mum's teach them not to play with their food?" Jack asked.

"Apparently not." John shrugged "Ronon survived for years, but he doesn't talk much about it. But he's a magnificent warrior and he wants to fight the Wraith."

Hermione and Ginny got a room to share, next to Harry and Ron. The four of them left their quarters together.

"So, I guess Harry and I are stuck here, while you go off on some dangerous mission." Ginny said.

"Ginny, it's only a reconnaissance mission." Ron argued.

"Actually, I'd rather stay with Sam and Janet." Hermione said and looked at Ginny "They're really great. And this is Merlin's city. Imagine the knowledge the libraries here must contain."

"Bloody hell 'Mione, you're in another galaxy and you're thinking about reading."

"And you're probably already thinking about the local food you hope to try out." Hermione replied with a snort.

Harry chuckled.

"Ginny, I'm rather pleased that I won't be the one sent off on some dodgy mission. And I get to be with you."

"I know Harry. It's just that the last time I was left behind, to be kept safe, I ended up fighting the Death Eaters at Hogwarts all year." Ginny said.

"This city is probably safer that Hogwarts, the Unspeakables have seen to that." Hermione said.

They soon parted as Harry and Ginny headed for the lag, while Ron and Hermione continued to the briefing room.

The briefing was rather formal gathering. It turned out that one of Teyla's contacts had sent a message. The contact wanted to meet and share information about the dead hive.

"I don't have to tell you to be careful." Dr Weir finished.

"Gear up then. We leave in 20 minutes." Shepperd said.

"Are you sure we should bring the children?" Ronon asked nodding to Ron and Hermione.

Shepperd had realised that Ronon would raise this objection and was prepared for it.

"Hermione. Would you be kind enough to fight with Ronon, but please make sure he'll be fit to join us on the mission?" Shepperd asked.

Ronon looked dubiously at Shepperd.

"I don't want to hurt her." he said.

"You won't" Jack said, supporting John "Trust me."

"Indeed." Teal'c added, who had learned the hard way, in friendly fights against Gawain, that fighting a wizard or witch wasn't easy.

Ronon, several inches taller than Ron, got up and assumed a fighting stance. Hermione stood up and faced him with her wand in her hand.

"Are you sure about this John?" Dr Weir asked.

"Yes, it's the only way they will earn Ronon's respect." John said and looked at the two "Begin."

Ronon attacked.

"Accio gun. Levicorpus." Hermione said and hoisted Ronon up in the air as she caught his gun.

"Our wizarding friends are so cool." Jack said with a smile.

"Is this enough?" Hermione asked looking at John.

"Actually, I haven't seen all the neat things Jack is bragging about." he replied "Please continue."

Hermione shrugged and made a demonstration on the helpless Ronon. She transfigured him into a rabbit and back, hit him with a tickling hex, released him to the floor and cast a jelly-leg jinx as soon as he tried to stand up. Ronon fell to the floor howling with laughter. After this Hermione released him.

"And that was only some basic transfiguration and prank hexes." Hermione told him.

Ronon darkened for a few moments, as if he considered attacking her again. But he realised he wasn't made fun of. This youngster was indeed a warrior worthy of his respect.

"I'm glad you're on our side." he said and relaxed "I'll be honoured to fight next to you."

"That's settled then." Dr Weir smirked "Now, get ready."

At the designated time the team moved out. Teyla, Teal'c and Ronon taking the lead, followed by Ron and Hermione, with Jack and John after them. Emerging on the other side of the wormhole Teyla met her contact who was waiting for them.

"This is Ina'an." he'll take us to his home, where his source is waiting. It's about 30 minutes to walk" she told.

"Lead the way." John said.

They walked on a road with fields on both sides and the sun shone from a blue sky. A nearby gas giant was also visible despite it was day.